1. Field of the Invention
The present invention relates to a movable contact unit to be used for operating a variety of electronic apparatuses, and a switch using the same movable contact unit.
2. Background Art
In recent years, a variety of electronic apparatuses including portable communication apparatuses such as portable phones have required an easy-to-use and inexpensive operating section. A movable contact unit used in a conventional operating section and the switch employing the movable contact unit are described with reference to FIGS. 9 and 10.
FIG. 9 shows a sectional view of a conventional movable contact unit, and FIG. 10 shows a sectional view of a switch employing the movable contact unit shown in FIG. 9. Movable contact unit 30 includes base sheet 31, movable contact 33, and pushing protrusion 34. Base sheet 31 is made of polyethylene terephthalate (PET) resin film, and has adhesive layer 32 at its underside. Movable contact 33 is made of resilient thin metal plate such as stainless steel, and shapes like a dome open downwardly and bowing upwardly. Movable contact 33 is held at a given place of base sheet 31 with its top face adhering to adhesive layer 32. A plurality of movable contacts 33 is thus constructed. Pushing protrusion 34 is stuck by adhesive 35 on the top face of base sheet 31 at a place corresponding to the domed top of movable contact 33. The most part of protrusion 34 is formed of PET resin. Adhesive 35 is an ultraviolet cure one made from urethane acrylate. Base sheet 31 and pushing protrusion 34 have resin layers 31A and 34A made of ester-based resin at their adhering faces, respectively.
Base sheet 31 has separator 36 stuck with adhesive layer 32 made from an insulating film to its underside for transporting and storing the movable contact unit 30. When movable contact unit 30 is to be in use, remove the separator 36 and stick movable contact unit 30 to wiring board (hereinafter simply referred to as “board”) 40, as shown in FIG. 10, by using adhesive layer 32 provided on the underside of base sheet 31. Board 40 has pairs of fixed contacts on its top face. Each pair is formed of center fixed contact 41 and outer fixed contact 42, and the pairs are prepared at places corresponding to respective movable contacts 33. Movable contact unit 30 is stuck to board 40 as discussed above, whereby switch 50 is formed.
Switch 50 is constructed such that the domed top of movable contact 33 is opposite to center fixed contact 41 with a space in between and the lower end of outer periphery of movable contact 33 seats on outer fixed contact 42. Movable contact 33 and a pair of fixed contacts 41, 42 form one switch, and a plurality of the switches forms panel switch 50 to be operated. Operating button 43 of an electronic apparatus is placed over pushing protrusion 43 seating on base sheet 31.
Operation of switch 50, which employs conventional movable contact unit 30 discussed above, is described hereinafter. First, a user pushes button 43 with his/her finger to lower button 43, and then the pushing force is applied to pushing protrusion 34 solidly contacting button 43, and the pushing force is further applied to the top of domed movable contact 33 via base sheet 31. When the pushing force becomes greater than another pushing force that resiliently reverses movable contact 33, the domed section of movable contact 33 reverses inside out, i.e. bowing downwardly, with a click feeling. This reversing allows the underside of the domed top to touch center fixed contact 41, so that fixed contact 41 becomes electrically conductive to fixed contact 42 via movable contact 33.
Release of the pushing force applied to button 43 weakens the another pushing force applied to movable contact 33 via pushing protrusion 34 and base sheet 31, and when this another pushing force becomes smaller than the restoring force of the domed section of movable contact 33 to the original position, movable contact 33 restores to the original domed shape (bowing upwardly) with a click feeling. Movable contact 33 thus leaves center fixed contact 41, and fixed contact 41 is insulated again from fixed contact 42.
Pushing protrusion 34 is placed such that movable contact 33 can be always pushed at its domed top center even if operating button 43 presses a place deviating from the center. This structure allows the click feeling, generated at the reversing and the restoring of movable contact 33, to be stable, so that a good tactile feeling of operation is obtainable.
Base sheet 31, in general, is made of PET resin of which breaking strength is in 200-260 MPa and breaking extension is in 80-140%. In other words, PET resin is a rather hard material, so that the click feeling generated at the resilient reversing of movable contact 33 is degraded. Because movable contact 33 is pressed via base sheet 31 made of PET resin, so that base sheet 31 needs some force to deform itself. When base sheet 31 includes electro luminance elements (EL elements) formed on its underside, the foregoing phenomenon becomes more remarkable.
To prevent the click feeling from being degraded, rather thin base sheet 31 is used, namely, its thickness is in 25 μm-75 μm. Use of a base sheet thinner than this range will damage base sheet 31 when EL elements are printed or sheet 31 is stuck to board 40. There is thus some limit to the improvement of the click feeling at the operation of switch 50.